1. Field of the Invention
Embodiments of the present invention relate to recording and/or reproducing apparatuses with signal quality determining devices and methods therefor, and more particularly, to methods devices for determining the quality of RF signals obtained from an optical disc.
2. Description of the Related Art
Binary data recorded on an optical disc can be reproduced by a recording and/or reproducing apparatus, having the capability to receive, convert, and analyze a reflected light beam, e.g., converting a light beam reflected from the optical disc into an electrical signal, performing a predetermined signal processing process on the electrical signal, and reproducing the information. The signal obtained by converting the light beam reflected from the optical disc into the electrical signal is called a radio frequency (RF) signal. Even though the data recorded on the optical disc is binary data, the RF signal obtained from the optical disc is an analog signal, due to the characteristics of the optical disc and optical characteristics. Therefore, a binarization process is required to convert the analog signal into a binary signal.
FIG. 1 is a block diagram of a conventional binarization device. This conventional binarization device includes a comparator 110 and a lowpass filter 130. The comparator 110 outputs a binary signal by binarizing an input RF signal based on a standard value provided by the lowpass filter 130. The binary signal output from the comparator 110 is provided to a phase locked loop (PLL) (not shown) to generate a system clock. Here, the RF signal and the system clock are not exactly synchronized, and there is a small phase difference between the RF signal and the system clock. This phase difference effect is called jitter.
FIGS. 2A and 2B illustrate jitter generated according to a conventional technology. In the ideal case, an edge of the system clock exactly meets a zero crossing point of the RF signal, as shown in FIG. 2A. However, in actuality, the edge of the system clock does not meet the zero crossing point of the RF signal, and the jitter is evident, as shown in FIG. 2B.
According to conventional techniques, the jitter value, which is the phase difference between an RF signal and a system clock, can be used as a barometer to evaluate the quality of the RF signal. That is, since the jitter value is larger when a large amount of noise is included in the RF signal, the quality of the RF signal can be obtained by measuring the jitter value.
However, as the data recording density of the optical disc increases, the magnitude of the RF signal has become smaller. In this case, since signal distortion is relatively large even when a small amount of noise is present, the jitter value will be large. Also, as the data recording density of the optical disc increases, more zero crossing points are included in the RF signal. Accordingly, a jitter circuit may malfunction.